34 research outputs found
Recommended from our members
Summary of Bureau of Economic Geology Pantex Plant 1992 Drilling Program
Two stratigraphic/hydrologic test wells were recently drilled on the Pantex plant by Fugro Geosciences, Inc., under contract to the Bureau of Economic Geology (BEG). This work, which is described in Task 9 of Appendix C--Annual Supplement to Scope of Work (1991-1992), was completed on April 13, 1992. These wells were completed as a perched aquifer observation well and as an Ogallala aquifer observation well. The following is a summary of the drilling program, the hydrologic and geologic findings, and the engineering problems encountered during drilling.Bureau of Economic Geolog
Recommended from our members
Hydrologic and Hydrochemical Data Compilation for Playa 5 and Pantex Lake
This report focuses on 2 wells near Playa 5 that have been sampled recently by the Bureau of Economic Geology (Figure 1). Each of these wells is located approximately 2,000 ft from the margin of the floor of Playa 5. On the basis of geochemical analyses, it appears that these wells are completed in the Ogallala aquifer rather than in perched aquifer(s). The well belonging to Mr. and Mrs. Cleo Kirkland, west of Playa 5 across F.M. 683, was sampled in August 1993, whereas the well of Mr. and Mrs. Sam McGregor, south of Playa 5 across U.S. 60, was sampled in May 1993. Sucker rods and service pipe were pulled from the Kirkland well on August 12, 1993, and the static water level was measured as 266.27 ft below land surface. Given an approximate land surface elevation (taken from the Sevenmile Basin topographic sheet) as 3,535 ft above sea level, the water level elevation in the Kirkland well is approximately 3,268.73 ft. For the McGregor well, the static water level on November 4, 1985, taken from the drillers' log, was 232 ft. Given an approximate land surface elevation of 3,510 ft, the water level elevation at that time was approximately 3,278 ft.Bureau of Economic Geolog
Recommended from our members
Hydrologic Characterization of Ground Water Resources in South Central Hudspeth County, Texas
Regional and local hydrologic investigations have been conducted in Trans-Pecos Texas at the principal study area for a low-level radioactive waste repository. The area is approximately 40 mi (65 km) southeast of El Paso in the Hueco Bolson, a fault-bounded desert basin that developed in the late Tertiary. Groundwater in the principal study area is found in Hueco Bolson silts and sands at depths of 361 ft (110 m) and 478 ft (146 m), and at depths of 592 ft (180 m) in Cretaceous limestones. The unsaturated zone consists of approximately 50 ft (15 m) of alluvial silt, sand, and gravel underlain by 300 to 500 ft (91 to 152 m) of lacustrine and fluvial clay, silt, and fine sand. The scope of this investigation included (1) evaluating groundwater resources in the area, (2) determining groundwater flow paths and velocities, and (3) testing hydrologic hypotheses using groundwater flow models.
Development of groundwater resources in the vicinity of the principal study area is limited by two key factors: (1) costs of drilling and completing wells and of producing water at depths typically greater than 400 ft (122 m), and (2) the very low productivity of aquifers. Transmissivities of aquifers in bolson and Cretaceous strata, as revealed by 11 aquifer tests, range from approximately 0.19 to 290.0 ft²/d (0.018 to 26.9 m²/d); corresponding permeabilities range from 0.0015 to 2.82 ft/d (0.0005 to 0.861 m/d). A composite potentiometric surface based on water levels measured in all available wells and on the hydrologic interconnection of the Diablo Plateau aquifer, Hueco Bolson silt and sand aquifer, and Rio Grande alluvium aquifer indicates that groundwater is recharged on the Diablo Plateau and flows to the south and southwest toward the Rio Grande beneath the bolson pediment. The inferred distribution of permeability zones focuses flow from the eastern Diablo Plateau toward Cretaceous outcrops along the Campo Grande fault, creating an observed potentiometric high. The relatively low hydraulic heads near the principal study area are caused by preferential drainage along relatively permeable bolson deposits to the west and southwest toward the Rio Grande. Water chemistry data, particularly on tritium, carbon-14, and total dissolved solids, generally support the interpreted flow pattern; some discrepancies can be related to paleohydrologic effects associated with the incision of the Rio Grande during Quaternary time.Bureau of Economic Geolog
Recommended from our members
Preliminary Findings on the Inorganic Geochemical Evolution of Ground Water in the Vicinity of the Pantex Plant
Since 1991, the Bureau of Economic Geology has sampled 29 wells in the vicinity of the Pantex Plant for hydrochemical analyses (Figure 1). Analyses were conducted of the following constituents (Tables 1 and 2): dissolved metals (cations), metalloids, anions, and inorganic carbon; ammonia; stable isotopes (deuterium [2H], boron-11, carbon-13, nitrogen-15, oxygen-18, and sulfur-34); radiogenic isotopes (tritium [3H] and carbon-14); and unstable parameters such as temperature, Eh (oxidation-reduction potential), pH, alkalinity (as bicarbonate), and dissolved oxygen. Nine of the wells sampled are located in one or more perched aquifers (referred to subsequently as the perched aquifer[s]) above the Ogallala aquifer water table: two private wells off-site (one to the north of the Pantex Plant, one to the west) and seven monitoring wells on-site. In the Ogallala aquifer itself, 19 wells were sampled: nine private wells upgradient from the Pantex Plant (two to the southwest, seven to the south) and ten wells on-site (six water-supply wells and four monitoring wells). In addition, we sampled a nearby private well identified by the Texas Water Development Board as being completed in the underlying (Permian-age) Quartermaster Formation. In the perched aquifer, three wells have been sampled three times and one has been sampled twice; in the Ogallala aquifer, four wells have been sampled three times and two have been sampled twice.Bureau of Economic Geolog
Recommended from our members
Geochemical Modeling of Ground Water in the Vicinity of the Pantex Plant, Southern High Plains, Texas
The Ogallala (High Plains) aquifer is the largest aquifer in the United States (Zwingle, 1993). Beneath the Southern High Plains of Texas, pumpage for irrigation and, to a lesser extent, for municipal, industrial, and domestic uses since the 1930s has caused water levels in the aquifer to decline locally more than 30 m (Knowles and others, 1982; Dugan and others, 1994). These declines have motivated numerous physically based studies of rates and sources of recharge to the Ogallala aquifer, as reviewed by Mullican and others (1994). However, hydrochemical studies have been fewer. Hydrochemical studies can complement physically based studies by delineating sources of recharge and rates of subsurface water movement as well as by elucidating controls on water quality. In particular, studies of compositional evolution during recharge to and flow within the Ogallala aquifer, such as have been conducted for other regional aquifers in North America (for example, Hendry and Schwartz, 1990; Plummer and others, 1990; Murphy and others, 1992), have been limited. In this report, we discuss the results of solute-speciation modeling involving data from wells sampled by the Bureau of Economic Geology (BEG) in the vicinity of the Pantex Plant (fig. 1). For a subset of these wells, solute data and data on the isotopic compositions of waters, soil gases, and sediments have been entered into a reaction-path (net mass-transfer) model. We use speciation and reaction-path modeling together to (1) corroborate inferred sources of recharge, (2) constrain estimates of travel times through the unsaturated zones above and below the perched aquifers, and (3) identify plausible reactions controlling the composition of groundwater.Bureau of Economic Geolog
Recommended from our members
Ground Water Hydrochemistry in the Southeastern Hueco Bolson and Southwestern Diablo Plateau, Trans-Pecos Texas
The hydrochemical history of groundwater in the arid southeastern Hueco Bolson and southwestern Diablo Plateau was investigated by collecting soil-moisture samples from unsaturated siliciclastic bolson-fill sediments and groundwater samples from the Diablo Plateau aquifer, the Hueco Bolson silt and sand aquifer, and the Rio Grande alluvial aquifer. Major, minor, and trace solutes, stable isotopic compositions, and activities of tritium and carbon-14 were measured in groundwater samples; major solute concentrations were determined in soil-moisture samples. Soil samples were collected to determine the type and amount of material that could be readily dissolved by recharge water. Core samples of Cretaceous carbonate and bolson-fill material were analyzed to determine the mineralogy of sediment and aquifer matrix.
The Hueco Bolson and Diablo Plateau aquifers contain mainly sodium-sulfate groundwater that derived solutes by calcite, dolomite, and gypsum dissolution, coupled with exchange of aqueous calcium and magnesium for sodium on clay minerals and other ion-exchange sites. Rio Grande groundwater is dominated by sodium and chloride derived from dissolution of salts precipitated in irrigated fields during times of high evaporation. All groundwaters are inferred to acquire major compositional characteristics early in the flow history, principally through reactions in the unsaturated zone.
Ages estimated from tritium and carbon-14 activities show that Rio Grande groundwaters are youngest, reflecting the short flow paths from the river to sampled wells following irrigation and percolation. Young groundwater is also found in the Diablo Plateau aquifer at wells both on the plateau and near the toe of the plateau escarpment. These are inferred to be recharge waters that rapidly moved along fractures to the water table. Other groundwater samples from the Diablo Plateau and Hueco Bolson aquifers are as much as 28,000 years old. Carbon-14 ages and tritium activities do not vary uniformly along a flow path. However, the oldest waters are found in wells near the center of the bolson pediment, and the distribution of carbon-14 ages generally conforms to the salinity distribution, suggesting a systematic relation between residence time, chemical and isotopic composition of groundwater, and regional hydrologic properties of the aquifers.Bureau of Economic Geolog
Recommended from our members
Delineating Controls on the Compostition of Ground Water in the Vicinity of the Pantex Plant, Southern High Plains, Texas
Chemical, isotopic, mineralogical, and bacteriological analyses indicate that the composition of groundwater in the vicinity of the Pantex Plant reflects distinctive sources of recharge (both natural and anthropogenic) modified by initial evaporation, sediment-water interactions, and microbial processes. As observed regionally by others, the major-ion fades are predominantly Ca-Mg-HCO3, reflecting ion exchange; dissolution of feldspars, calcite, sepiolite, palygorskite, and CO2 gas; precipitation of calcite, Na- and Ca-smectite, sepiolite, and palygorskite; exsolution of CO2 gas; and oxidation of organic carbon. Above-background concentrations of Cl- and NO3- indicate return flow of wastewater, although NO3- exceeds the drinking-water standard in only one well. NO3- concentrations tend to be limited during recharge by microbially mediated denitrification in the vadose zone beneath playas.
Elevated levels of 3H and 14C indicate focused recharge beneath both playas and ditches. Focused recharge is also indicated by values of δD and δ18O that are enriched beneath playas. The coincidence of plots of δD versus δ18O with local seasonal meteoric water lines suggests minimal evaporation, which may reflect episodic recharge or recharge along preferential pathways. Depleted δD and δ18O of H2O and enriched δ13C of dissolved inorganic carbon indicate some diffuse infiltration to perched aquifers in interplaya areas, although the timing of such recharge is uncertain. Dissolved Si and 14C provide evidence of percolation from the perched aquifers to the Ogallala aquifer beneath the Pantex Plant.Bureau of Economic Geolog
Recommended from our members
Hydrologic Investigations of the Saturated Zone in South Central Hudspeth County, Texas
Hydrologic investigations are in progress in Trans-Pecos Texas at the proposed site of a low-level radioactive waste repository. The site is approximately 40 mi (65 km) southeast of El Paso in the Hueco Bolson, a fault-bounded desert basin that developed in the late Tertiary. Groundwater in the area of the proposed site is found at depths of 478 ft (146 m) and 592 ft (180 m) in bolson silt and sand and Cretaceous limestone, respectively. The unsaturated zone consists of approximately 50 ft (15 m) of alluvial silt, sand, and gravel underlain by 450 ft (137 m) of lacustrine and fluvial clay, silt, and fine sand.
High-priority tasks for characterizing the groundwater regime include (1) evaluating groundwater resources in the area, (2) determining groundwater flow paths and velocities, (3) testing hydrologic hypotheses using groundwater flow models, and (4) determining groundwater hydrochemistry. The objective of this report is to evaluate the groundwater resources and to discuss our current understanding of groundwater flow paths and velocities.
Groundwater resources in the vicinity of the site are limited by two key factors: (1) costs of drilling and completing wells and of producing water at depths greater than 400 ft (122 m) and (2) very low productivity of aquifers. Typical transmissivities of aquifers producing from bolson and Cretaceous strata, based on four tests, range from approximately 4.3 x 10^-2 ft²/day (4.0 x 10^-3 m²/day) to 2.9 x 10^2 ft²/day (2.7 x 10^1 m²/day). A composite potentiometric surface has been mapped on the basis of static water levels measured in all available wells. Regional groundwater flow is interpreted from the potentiometric surface to be generally south-southwest toward the Rio Grande.Bureau of Economic Geolog
Recommended from our members
Ground Water Hydrochemistry in the Southeastern Hueco Bolson,Trans-Pecos Texas
The hydrochemical history of groundwater in the arid southeastern Hueco Bolson was investigated by collecting soil-moisture samples from unsaturated siliciclastic bolson-fill sediments and groundwater samples from the Diablo Plateau aquifer, the Hueco Bolson silt and sand aquifer, and the Rio Grande alluvial aquifer. Major, minor, and trace solutes, stable isotopic compositions, and activities of tritium and carbon-14 were measured in groundwater samples, while major solute concentrations were determined in soil-moisture samples. Soil samples were collected to determine the type and amount of material that could be readily dissolved by recharge water. Core samples of Cretaceous carbonate and bolson-fill material were analyzed to determine the mineralogy of sediment and aquifer matrix.
The Hueco Belson and Diablo Plateau aquifers predominantly contain Na-SO4 groundwater, derived from solutes through carbonate and gypsum dissolution, coupled with the exchange of aqueous calcium and magnesium for sodium on clay minerals and other ion exchange sites. Rio Grande groundwater is dominated by sodium and chloride, derived from the dissolution of salts precipitated in irrigated fields during periods of high evaporation. Major compositional characteristics of all groundwater types appear to be acquired early in the flow history, primarily through reactions in the unsaturated zone.
Ages estimated from tritium and carbon-14 activities indicate that Rio Grande groundwater is the youngest, reflecting short flow paths from land surface following irrigation, infiltration, and deep penetration from the river to sampled wells. Groundwater from the Diablo Plateau and Hueco Bolson aquifers ranges in age from a few hundred to nearly 29,000 years. Carbon-14 ages and tritium activities do not vary systematically along a flow path; however, the oldest waters are found in wells near the center of the bolson pediment. The irregular distribution of carbon-14 and tritium suggests that the Bolson and Diablo Plateau aquifers are internally complex, and flow velocities are not readily predictable solely based on the potentiometric gradient and estimates of regional porosity and permeability data.Bureau of Economic Geolog
Recommended from our members
Technical Issues for Chemical Waste Isolation in Solution-Mined Caverns in Salt Domes
Many factors contribute to assessing the technical viability of isolating chemical waste in solution-mined caverns within salt domes. Our investigation highlights several key factors of primary importance, including geohydrology, engineering considerations, and the stability of the geologic isolation system, encompassing the cavern, cap rock, and surrounding strata. These factors are largely interconnected and mutually dependent.
An essential initial step involves detailed mapping of the domal system, including the cap rock, salt stock, and surrounding domed strata, a level of detail often lacking in public sources and geological literature. Postulated release scenarios typically involve waste transport via groundwater, making the direction and rates of groundwater flow critical. Groundwater flow is influenced by various factors such as rock matrix composition, depositional systems, sand-body geometry, and fault patterns.
The cap rock serves as a focal point for many domal processes and is a dynamically changing region of a salt dome. Studies on cap-rock properties can help determine whether salt domes are undergoing uplift or dissolution. The cap rock plays a crucial role in either facilitating or impeding dome dissolution and cavern stability. Further research on salt domes should focus on defining the geometry and structure of cap rocks, identifying cap-rock lost-circulation zones, understanding the geometry, structure, and stratigraphy of salt stocks and caverns, assessing salt-cavern stability, and investigating domal geohydrology.
In the following sections, we discuss various issues that need to be addressed to evaluate the technical feasibility of isolating chemical waste in solution-mined caverns within salt domes.Bureau of Economic Geolog